What causes this?

To find out, we used salinity and \(\delta ^{18}O\) of lagoon waters sampled in April (full sea ice cover), June (sea ice break-up), and August (open water summer). Explore the data in the plot below:

We used the distinct salinity and \(\delta ^{18}O\) values of sea ice melt (SIM), marine Polar Mixed Layer (PML), and meteoric water (MW) to determine the relative contribution of each endmember to these dynamic lagoons.

\(\delta ^{18}O\) of MW actually varies longitudinally, as seen by the pattern in freshwater inflow samples, here with stations ordered west->east:

Lagoon	riv_d18O	sd
Elson	-12.92	0.83
Simps	-17.35	0.07
Stef	-20.25	0.35
Jago	-21.40	NaN

We solved the following system of equations for each lagoon water sample:

\(SIM+MW+PML = 1\)

\(5*SIM + 0*MW + 32.1*PML = Salinity\)

\(-2*SIM + x*MW + -3.5*PML = \delta ^{18}O\)

where \(x\) is the mean value for rivers associated with a particular lagoon (see above table)

The results of our mixing model (below) show how source waters stratify and/or mix in each lagoon over the year.

Values beyond 100 are due to hypersalinity in the winter, caused by brine exclusion during sea ice formation. This causes salinity to go beyond the end-member value.

What have we learned?

*At break-up, both SIM and MW usually contribute to the large drops in salinity, but it varies by lagoon system

Beaufort Lagoon source waters - poster

Christina Bonsell and Emily Bristol

Jan 18, 2020

The Beaufort Lagoon Ecosystems Long-Term Ecological Research program (BLE LTER) samples lagoons and coastal areas across the Beaufort Sea coast

We have 4 stations per lagoon system, two in shallow reaches of the lagoon (<1m), and two in deeper areas (>3m). We also sample major freshwater inflows associated with each lagoon.

These lagoons exhibit large variability in salinity over the year.